Griffith's theory of failure is based on the assumption that the low order
of tensile strength in common materials is due to the presence of small
cracks or flaws. Actual stresses may occur around these flaws, which are
of the order of magnitude of molecular cohesion values, while the average
tensile strength may be quite low. Mohr's theory predicts that failure of
materials is due to failure in shear, whereas Griffith's theory postulates
that it is due to failure at crack tips. Lewis
A joint fracture in limestone, widened by solution.
a. Grindability of coal, or the ease with which it may be ground fine
enough for use as pulverized fuel, is a composite physical property
embracing other specific properties, such as hardness, strength, tenacity,
and fracture. Mitchell
b. The effect produced on representative pieces of ore by applying
standard methods of comminution, assessed comparatively in terms of size
reduction and power used. Pryor, 4
c. Relative ease of grinding, analogous to machinability. ASM, 1
A measure of the grindability of a material under specified grinding
conditions, expressed in terms of volume of material removed per unit
volume of wheel wear. ASM, 1
a. In ore dressing, smelting, and refining, one who mixes raw materials,
such as bauxite, lime, soda ash, and starch, entering the
alumina-extraction process to produce a slurry of proper chemical
composition, using a ball mill. Also called ball mill operator.
DOT
b. In ore dressing, smelting, and refining, one who grinds ore and
separates fine particles from coarse particles in a ball mill and
classifier arranged in continuous series. DOT
Disease of the lungs consequent upon inhaling the metallic dust produced
in grinding operations. Also called grinders' rot; phthisis.
Standard, 2
a. Size reduction into fine particles; comminution.
See also:dry grinding; wet grinding.
b. The process of erosion by which rock fragments are worn down, crushed,
sharpened, or polished through the frictional effect of continued contact
and pressure by larger fragments. AGI
c. Abrasion by rock fragments embedded in a glacier and dragged along the
bedrock floor. AGI
An additive to the charge in a ball mill or rod mill to accelerate the
grinding process; the additive has surface-active or lubricating
properties. Grinding aids find particular use in the grinding of portland
cement clinker but, in the United Kingdom, their use is precluded by the
conditions laid down in British Standard 12. Dodd
The sequence of operations in grinding a material, including, for example,
the screening of the primary product and the recirculation of the screen
overflow. BS, 5
A machine for the wet or dry fine crushing of ore or other material. The
three main types are the ball, rod, and tube mills. The mill consists of a
rotating cylindrical drum; the ore enters one hollow trunnion and the
finished product leaves the other. Modern practice indicates ball mill
feeds of 1/2 in, 3/4 in, and 1 in (1.27 cm, 1.91 cm, and 2.54 cm) for
hard, medium, and soft ores respectively and the products range from 35 to
200 mesh and finer. See also:open-circuit mill
Pebbles, usually of chert or quartz, used for grinding in mills where
contamination with iron must be avoided.
A French marble of a beautiful red color and often variegated with small
dashes of purple and spots or streaks of white, as in the variety locally
known as griotte oeil de perdrix from the French Pyrenees. Fay
A strap brake or ribbon brake on a hoisting apparatus. Standard, 2
One whose direction is inclined away from the adjacent free face, or may
be defined as one whose width is greater at the toe than at the heel.
Zern
A shot so placed that the point or inner end of the hole is considerably
farther from the face of the coal to be broken than is the heel or outer
end of the hole. See also:shot
When a cut is so made by a mining machine or a shot is so placed by a
miner that the cut or shot enters the coal beyond the proper line of the
rib, it is said to grip the rib. Zern
See:grizzly
a. A coarse-grained sandstone, esp. one composed of angular particles;
e.g., a breccia composed of particles ranging in diameter from 2 to 4 mm.
AGI
b. A sand or sandstone made up of angular grains that may be coarse or
fine. The term has been applied to any sedimentary rock that looks or
feels gritty on account of the angularity of the grains. AGI
c. A sandstone composed of particles of conspicuously unequal sizes
(including small pebbles or gravel). AGI
d. A sandstone with a calcareous cement. The term has been applied
incorrectly to any nonquartzose rock resembling a grit; e.g., pea grit or
a calcareous grit. AGI
e. A small particle of a stone or rock; esp. a hard, angular granule of
sand. Also, an abrasive composed of such granules. AGI
f. The structure or grain of a stone that adapts it for grinding or
sharpening; the hold of a grinding substance. Also, the size of abrasive
particles, usually expressed as their mesh number. AGI
g. An obsolete term for sand or gravel, and for earth or soil. The term is
vague and has been applied widely with many different connotations.
Etymol: Old English greot, gravel, sand. AGI
An adaptation of any of several types of conveyors used for removing heavy
solids from settling tanks or basins. See also:bucket elevator;
flight conveyor; reciprocating flight conveyor; screw conveyor.
See:mesh number
In quarrying, a process that gives a smoother surface than rubbing. It is
accomplished with silicon carbide or aluminum oxide abrasive bricks
attached to revolving buffer heads. AIME, 1